BURROWING MAYFLIES OF OUR LARGER LAKES AND STREAMS. 
2 
By James G. NEEDHAM, 
Professor of Limnology, Cornell University. 
& 
INTRODUCTION. 
In the beds of all our larger lakes and streams there exists a vast animal popula- 
tion, dependent, directly or indirectly, upon the rich organic food substances that are 
bestowed by gravity upon the bottom. Many fishes wander about over the bottom for- 
aging. Many mollusks, heavily armored and slow, go pushing their way and leaving 
trails through the bottom sand and sediment. And many smaller animals burrow, 
some by digging their way like moles, as do the young of mayflies and of gomphine 
dragonflies; some by ‘“‘worming”’ their way through the soil, as do the larve of crane 
flies and many oligochetes. 
Among the burrowers none are more abundant or more important than the young 
of the mayflies. Indeed, there are hardly any aquatic organisms of greater economic 
value, for they are among the principal herbivores of the waters, and they are all choice 
food for fishes. 
How abundant they are in all our large lakes and streams is well attested by the 
vast hordes of adults that appear in the air at the times of their annual swarming. They 
issue from the water mainly at night. They fly away to the banks and settle upon 
the shore vegetation. They cover the sides of buildings. They fly heedlessly into the 
faces of pedestrians. They settle upon the stream-side willows until their accumulated 
weight bends, and often breaks, the boughs. In the streets of riparian cities they fly to 
lights at night and fall beneath them in heaps upon the ground. Their bodies, crushed 
under the wheels of cars, render the rails slippery, sometimes impeding traffic. They 
feed a host of carnivores, terrestrial, aerial, and aquatic; indeed, many birds and fishes 
gormandize rather shockingly during their swarming season. And when those that have 
escaped both foes and casualties have conveyed their eggs back into their native waters, 
their bodies fall at last upon the surface and drift about. After the surfeited fishes can eat 
no more, the mayflies are blown into windrows upon the shores; or they drift in long 
lines that trail at the edges of the current in streams; or they gather in great masses and 
welter in the eddies. Sometimes they stop the river steamers by clogging the machinery. 
No dweller by the shores needs to be convinced of their abundance. 
That they abound also far out from the shore is well attested by certain observa- 
tions made by Commissioner Smith on Lake Erie nine years ago and later communi- 
eated in a letter. Dr. Smith wrote that, while making a cruise on a lighthouse tender 
which was visiting gas buoys in all parts of the lake, ‘‘Many of these buoys, especially 
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